The invention relates to active acoustic attenuation systems, and provides a system for shaping the attenuation of the output acoustic wave.
The invention particularly arose during continuing development efforts relating to the subject matter shown and described in U.S. Pat. No. 4,677,676, incorporated herein by reference. The invention also arose during continuing development efforts relating to the subject matter shown and described in U.S. Pat. Nos. 4,677,677, 4,736,431, 4,815,139, and 4,837,834, incorporated herein by reference.
Active attenuation involves injecting a canceling acoustic wave to destructively interfere with and cancel an input acoustic wave. In an active acoustic attenuation system, the output acoustic wave is sensed with an error transducer such as a microphone which supplies an error signal to a control model which in turn supplies a correction signal to a canceling transducer such as a loudspeaker which injects an acoustic wave to destructively interfere with and cancel the input acoustic wave. The acoustic system is modeled with an adaptive filter model having a model input from the input transducer such as a microphone, and an error input from the error microphone, and outputting the noted correction signal to the canceling speaker.
In the present invention, the error signal from the error transducer, e.g., error microphone, is specified to correspondingly specify the output acoustic wave.
In the present invention, the error signal is specified by summing the error signal with a desired signal to provide an error signal to the error input of the system model such that the model outputs the correction signal to the output transducer, e.g., speaker, to introduce the canceling acoustic wave such that the desired signal is present in the output acoustic wave. This provides a desired sound other than complete cancellation.